Air pollution is the introduction of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other

living organisms, or damages the natural environment, into the atmosphere. The atmosphere is a complex, dynamic natural gaseous system that is essential to support life on planet Earth. Stratospheric ozone depletion due to air pollution has long been recognized as a threat to human health as well as to the Earth's ecosystems. Ma or primary pollutants produced by human activity include!

Sulfur oxides "S#x$ % especially sulfur dioxide, a chemical compound with the formula S#&. S#& is produced by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide. 'urther oxidation of S#&, usually in the presence of a catalyst such as (#&, forms )&S#*, and thus acid rain.+&, This is one of the causes for concern over the environmental impact of the use of these fuels as power sources. (itrogen oxides "(#x$ % especially nitrogen dioxide are emitted from high temperature combustion. -an be seen as the brown haze dome above or plume downwind of cities.(itrogen dioxide is the chemical compound with the formula (#&. .t is one of the several nitrogen oxides. This reddish%brown toxic gas has a characteristic sharp, biting odor. (#& is one of the most prominent air pollutants. -arbon monoxide % is a colourless, odourless, non%irritating but very poisonous gas. .t is a product by incomplete combustion of fuel such as natural gas, coal or wood. /ehicular exhaust is a ma or source of carbon monoxide. -arbon dioxide "-#&$ % a greenhouse gas emitted from combustion but is also a gas vital to living organisms. .t is a natural gas in the atmosphere. /olatile organic compounds % /#-s are an important outdoor air pollutant. .n this field they are often divided into the separate categories of methane "-)*$ and non%methane "(M/#-s$. Methane is an extremely efficient greenhouse gas which contributes to enhanced global warming. #ther hydrocarbon /#-s are also significant greenhouse gases via their role in creating ozone and in prolonging the life of methane in the atmosphere, although the effect varies depending on local air 0uality. 1ithin the (M/#-s, the aromatic compounds benzene, toluene and xylene are suspected carcinogens and may lead to leu2emia through prolonged exposure. 3,4%butadiene is another dangerous compound which is often associated with industrial uses.

Sources of air pollution refer to the various locations, activities or factors which are responsible for the releasing of pollutants in the atmosphere. These sources can be classified into two ma or categories which are! Anthropogenic sources "human activity$ mostly related to burning different 2inds of fuel

5Stationary Sources5 include smo2e stac2s of power plants, manufacturing facilities "factories$ and waste incinerators, as well as furnaces and other types of fuel%burning heating devices 5Mobile Sources5 include motor vehicles, marine vessels, aircraft and the effect of sound etc. -hemicals, dust and controlled burn practices in agriculture and forestry management. -ontrolled or prescribed burning is a techni0ue sometimes used in forest management, farming, prairie restoration or greenhouse gas abatement. 'ire is a natural part of both forest and grassland ecology and controlled fire can be a tool for foresters. -ontrolled burning stimulates the germination of some desirable forest trees, thus renewing the forest. 'umes from paint, hair spray, varnish, aerosol sprays and other solvents 1aste deposition in landfills, which generate methane.Methane is not toxic6 however, it is highly flammable and may form explosive mixtures with air. Methane is also an asphyxiant and may displace oxygen in an enclosed space. 7sphyxia or suffocation may result if the oxygen concentration is reduced to below 38.9: by displacement Military, such as nuclear weapons, toxic gases, germ warfare and roc2etry

Natural sources

;ust from natural sources, usually large areas of land with little or no vegetation. Methane, emitted by the digestion of food by animals, for example cattle. <adon gas from radioactive decay within the Earth's crust.<adon is a colorless, odorless, naturally occurring, radioactive noble gas that is formed from the decay of radium. .t is considered to be a health hazard.<adon gas from natural sources can accumulate in buildings, especially in confined areas such as the basement and it is the second most fre0uent cause of lung cancer, after cigarette smo2ing. Smo2e and carbon monoxide from wildfires. /olcanic activity, which produce sulfur, chlorine, and ash particulates.

The 1orld )ealth #rganization states that &.* million people die each year from causes directly attributable to air pollution, with 3.9 million of these deaths attributable to indoor air pollution.+8, 5Epidemiological studies suggest that more than 9==,=== 7mericans die each year from cardiopulmonary disease lin2ed to breathing fine particle air pollution. . .5+3=, 7 study by the >niversity of ?irmingham has shown a strong correlation between pneumonia related deaths and air pollution from motor vehicles.+33, 1orldwide more deaths per year are lin2ed to air pollution than to automobile accidents.+citation needed, @ublished in &==9 suggests that 43=,=== Europeans die from air pollution annually. +citation needed, ;irect causes of air pollution related deaths include aggravated asthma, bronchitis,

emphysema, lung and heart diseases, and respiratory allergies.+citation needed, The >S E@7 estimates that a proposed set of changes in diesel engine technology "Tier 2$ could result in 3&,=== fewer premature mortalities, 39,=== fewer heart attac2s, A,=== fewer emergency room visits by children with asthma, and B,8== fewer respiratory%related hospital admissions each year in the >nited States.+citation needed, The worst short term civilian pollution crisis in .ndia was the 38B* ?hopal ;isaster.+3&, Cea2ed industrial vapors from the >nion -arbide factory, belonging to >nion -arbide, .nc., >.S.7., 2illed more than &,=== people outright and in ured anywhere from 39=,=== to A==,=== others, some A,=== of whom would later die from their in uries.+citation needed, The >nited Dingdom suffered its worst air pollution event when the ;ecember * Ereat Smog of 389& formed over Condon. .n six days more than *,=== died, and B,=== more died within the following months.+citation needed, 7n accidental lea2 of anthrax spores from a biological warfare laboratory in the former >SS< in 38F8 near Sverdlovs2 is believed to have been the cause of hundreds of civilian deaths.+citation needed, The worst single incident of air pollution to occur in the >nited States of 7merica occurred in ;onora, @ennsylvania in late #ctober, 38*B, when &= people died and over F,=== were in ured.+34, The health effects caused by air pollutants may range from subtle biochemical and physiological changes to difficulty in breathing, wheezing, coughing and aggravation of existing respiratory and cardiac conditions. These effects can result in increased medication use, increased doctor or emergency room visits, more hospital admissions and premature death. The human health effects of poor air 0uality are far reaching, but principally affect the body's respiratory system and the cardiovascular system. .ndividual reactions to air pollutants depend on the type of pollutant a person is exposed to, the degree of exposure, the individual's health status and genetics.+citation needed, 7 new economic study of the health impacts and associated costs of air pollution in the Cos 7ngeles ?asin and San Goa0uin /alley of Southern -alifornia shows that more than 4B== people die prematurely "approximately 3* years earlier than normal$ each year because air pollution levels violate federal standards. The number of annual premature deaths is considerably higher than the fatalities related to auto collisions in the same area, which average fewer than &,=== per year +3*,. ;iesel exhaust ";E$ is a ma or contributor to combustion derived particulate matter air pollution. .n several human experimental studies, using a well validated exposure chamber setup, ;E has been lin2ed to acute vascular dysfunction and increased thrombus formation.+39,+3A, This serves as a plausible mechanistic lin2 between the previously described association between particulate matter air pollution and increased cardiovascular morbidity and mortality.

Environmental impacts of greenhouse gas pollutants

Main articles! #cean acidification and Ereenhouse effect

The greenhouse effect is a phenomenon whereby greenhouse gases create a condition in the upper atmosphere causing a trapping of heat and leading to increased surface and lower tropospheric temperatures. -arbon dioxide from combustion of fossil fuels is the ma or problem. #ther greenhouse gases include methane, hydrofluorocarbons, perfluorocarbons, chlorofluorocarbons, nitrogen oxides, and ozone. This effect has been understood by scientists for about a century, and technological advancements during this period have helped increase the breadth and depth of data relating to the phenomenon. -urrently, scientists are studying the role of changes in composition of greenhouse gases from natural and anthropogenic sources for the effect on climate change. 7 number of studies have also investigated the potential for long%term rising levels of atmospheric carbon dioxide to cause increases in the acidity of ocean waters and the possible effects of this on marine ecosystems.